Acetals of 2-alkyl-3-norbornyl propanals

ABSTRACT

ACETALS OF 2-ALKYL-3-NORBORNYL PROPANALS OF THE FORMULA   2-((R2-O-)2-CH-CH(-R)-CH2-),3-R1-NORBORNANE   WHEREIN R AND R2 REPRESENTS LOWER ALKYL GROUPS AND R1 REPRESENTS HYDROGEN OR METHYL ARE PREPARED BY REACTING A 2-ALKYL-3-NORBORNYL PROPANAL WITH A LOWER ALKANOL IN THE PRESENCE OF THE CORRESPONDING ALKYL ESTER SELECTED FROM THE GROUP CONSISTING OF TRIALKYL ORTHOFORMATES, TETRAALKYL ORTHOSILICATES AND DIALKYL SULFITES AND A CATALYTIC AMOUNT OF A STRONG ACID, ION EXCHANGE RESIN OR AMMONIUM NITRATE. THE COMPOUNDS HAVE VERY PLEASANT FINE FRUITY, WINEY, WOODY AND TOBACCO AROMAS ARE ARE USEFUL AS COMPONENTS IN FRAGRANCE COMPOSITIONS.

United States Patent 3,803,244 ACETALS OF 2-ALKYL-3-NORBORNYL PROPANALS Alfred A. Schleppnik, St. Louis, Mo., assignor to Monsanto Company, St. Louis, M0. N0 Drawing. Filed Jan. 3, 1972, Ser. No. 215,188 Int. Cl. C07c 43/18 US. Cl. 260-611 F 8 Claims ABSTRACT OF THE DISCLOSURE Acetals of 2-alkyl-3-norbornyl propanals of the formula wherein R and R represent lower alkyl groups and R represents hydrogen or methyl are prepared by reacting a 2-alkyl-3-norbornyl propanal with a lower alkanol in the presence of the corresponding alkyl ester selected from the group consisting of trialkyl orthoformates, tetraalkyl orthosilicates and dialkyl sulfites and a catalytic amount of a strong acid, ion exchange resin or ammonium nitrate. The compounds have very pleasant fine fruity, winey, woody and tobacco aromas and are useful as components in fragrance compositions.

This invention relates to the art of fragrance compositions and, more particularly, to a novel class of compounds possessing characteristic aromas. More specifically, this invention is directed to a novel class of useful acetals, their preparation and the utility of these compounds as fragrances.

The art of perfumery began, perhaps, in the ancient cave dwellings of prehistoric man. From its inception, and until comparatively recently, the perfumer has utilized natural perfume chemicals of animal and vegetable origin. Thus, natural perfume chemicals such as the essential oils, for example, oil of rose and oil of cloves, and animal secretions such as musk, have been manipulated by the perfumer to achieve a variety of fragrances. In more recent years, however, research perfume chemists have developed a large number of synthetic odoriferous chemicals possessing aroma characteristics particularly desired in the art. These synthetic aroma chemicals have added a new dimension to the ancient art of the perfumer, since the compounds prepared are usually of a stable chemical nature, are inexpensive as compared with the natural perfume chemicals and lend themselves more easily to manipulation than the natural perfume chemicals since such natural perfume chemicals are usually a complex mixture of substances which defy chemical analysis. In contrast thereto, the synthetic aroma chemicals possess a known chemical structure and may therefore be manipulated by the perfumer to suit specific needs. Accordingly, there is a great need in the art of fragrance compositions for new compounds possessing specific characteristic aromas.

The principal object of the present invention is to provide a new class of aroma chemicals consisting of acetals of 2-alkyl-3-norbornyl propanals and to methods of preparing same.

Another object of the present invention is to provide a specific class of acetal compounds having a characteristic aroma which is utilized in the preparation of fragrances and fragrance compositions.

These and other objects, aspects and advantages of this invention will become apparent from a consideration of the accompanying specification and claims.

In accordance with the above objects, there is pro- 3,803,244 Patented Apr. 9, 1974 vided by the present invention a novel class of compounds characterized by the formula wherein R and R represent the same or different lower alkyl groups, i.e., an alkyl group of from 1 to 5 carbon atoms, and R represents hydrogen or methyl.

Representative alkyl groups characterized by R and R of the above formula include methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, tert-butyl, n-amyl, i-amyl, tertamyl and the like.

The novel compounds of this invention are prepared by reacting a 2-alkyl-3-norborny1 propanol characterized by the formula wherein R represents hydrogen or methyl and R represents a lower alkyl group of from 1 to 5 carbon atoms, e.g., methyl, ethyl, propyl, butyl, amyl and the like as described hereinbefore, with a lower alkanol, such as methanol. Such a reaction is illustrated by the following equation:

wherein R has the same meaning as defined hereinbefore. The above reaction is reversible so that it is necessary to either remove the water formed or chemically bind it so as to prevent the reverse reaction. It has been discovered that the latter can be done by carrying out the above reaction in the presence of the corresponding akyl ester selected from the group consisting of trialkyl orthoformates, tetraalkyl orthosilicates and dialkylsulfites. The term corresponding alkyl esters refers to those above named esters wherein the alkyl moieties of the ester correspond to the alkanol that is reacted with the 2-alkyl-3- norbornyl propanal. In this secondary reaction the water formed in reaction I reacts with the corresponding alkyl ester to form the alkanol and an ester with less alkyl moieties. Such a reaction is illustrated by the following equation (the illustrative ester is the orthoformate ester):

Obviously one could use alkyl esters that do not correspond to the alkanol utilized if one desired mixtures of acetals but this would present recovery problems.

The reactions should also be carried out in the presence of a catalytic amount of a strong acid, ion exchange resin or ammonium nitrate.

The 2-alkyl-3-norbornyl propanals described above include compounds such as Z-methyl-S-norbornyl propanal, 2-n-propyl-3-norbornyl propanal and 2-n-butyl-3-norbornyl propanal and the like. These propanal compounds can be prepared, as described in my copending patent application Ser. No. 103,879, filed Jan. 4, 1971, by the reaction of a 5-norbornene-2-carboxaldehyde or norbornane-Z-carboxaldehyde with an aliphatic aldehyde possessing an OL- methylene group, in a basic medium, followed by a dehydration of the aldol formed. The resulting compounds can then be hydrogenated to the 2 alkyl-3-norbornylpropanals.

Representative lower alkanols which are utilized in accordance with this invention include methanol, ethanol,

propanol, i-propanol, butanol, i-butanol, tert-butanol, namyl, i-amyl, tert-amyl and the like.

In a preferred embodiment of this invention, the 2- alkyl-3-norbornyl propanal is reacted with a lower alkanol, such as methanol, in the presence of the coresponding trialkyl orthoformate, such as trimethyl orthoformate. Alternatively, the alkanol can be ethanol the corresponding alkyl ester being triethyl orthoformate and the like.

Ordinarily the mixture of the propanal, alkanol, ester and catalyst is refluxed for varying lengths of time to afford the product of this invention. However, the reaction conditions are not critical but should be such as to facilitate the preparation of the product. Normally lower temperatures are preferred in carrying out the reaction; thus the reaction should normally be conducted at temperatures such as from about 25 C. to about 100 C.

The propanal and the alkanol which are reacted in accordance with this invention are preferably reacted in a mole ratio from about 1 to .5 to about 1 to 2; however, the mole ratio may be from about 1 to .1 to about 1 to 20 and still be satisfactory.

The ester should be present in at least equirnolar amounts based on the amount of propanal present.

The amount of catalyst included in the reaction is from about 0.01 to about 5.0 percent, based on the Weight of reactants present. Obviously the amount of catalyst added depends on the particular reactants and the specific reaction conditions employed.

The novel compounds of this invention are useful in the preparation and formulation of fragrance compositions such as perfumes and perfumed products due to their pleasing fine fruity, winey, woody and tobacco aromas. Perfume compositions and the use thereof in cosmetic, detergent and bar soap formulations and the like are exemplary of the utility thereof.

The compounds of this invention are used in concentrations of from trace amounts up to about 50 percent of the perfume composition into which they are incorporated. As will be expected, the concenration will vary depending on the particular fragrance composition and even within the same composition when compounded by different perfumers.

The following examples will serve to illustrate certain specific embodiments within the scope of this invention and are not to be construed as limiting the scope thereof.

EXAMPLE 1 1-1-diethoxy-2-methyl-3-norbornyl propane 19.52 g. of 2 methyl-3-norbornyl propanal was dissolved in 50 m1. of ethanol together with 18 g. tn'ethyl orthoformate followed by the addition of 100 mg. of ptoluenesulfonic acid. An exothermic reaction occurred with the liquid reaction mass turning an amber color. After 5 minutes no aldehyde could be detected by IR analysis. The reaction mass was maintained at 23-25 C. for three (3) hours. The reaction mass was diluted with ether, washed with 1% sodium hydroxide aqueous solution, water and brine and dried over sodium sulfate. Workup afforded 24.0 g. of a crude product; a yellowish liquid having a n :1.4563. The crude product was distilled through a short Vigreux column to give a colorless liquid 4 product having a boiling point of IOU-108 C. at 1 mm. of Hg and a n =1.4605. The material was submitted to a fragrance panel for aroma characterization and it was described as having fruity, nut-like, winey, woody, green and tobacco aromas. Upon analysis the product was determined to be 1,1 diethoxy 2-methyl-3-norbornyl propane.

EXAMPLE 2 1,1-dimethoxy-2-methyl-3-norbornyl propane Following a procedure similar to that utilized in Example 1, 2 methyl-3-norbornyl propanal is reacted with methanol in the presence of trimethyl orthoformate and a catalytic amount of p-toluene sulfonic acid. The resulting product is a colorless liquid having a boiling point of 66-69 C. at 0.2 mm. of Hg having a n =l.46l6. The aroma characteristies'are quite similar to those of the compound prepared in Example 1. Upon analysis the product was determined to be l,l-dimethoxy-2-methyl-3- norbornyl propane.

While this invention has been described hereinabove with regard to certain illustrative specific embodiments, it is not so limited since many modifications and variations are possible in the light of the above teachings. It is understood therefore that the invention may be practiced otherwise than as specifically described without departing from the spirit and scope of the invention.

The embodiments of this invention in which a particular property or privilege is claimed are defined as follows:

1. A compound characterized by the structural formula wherein R represents hydrogen or methyl and R and R represent a lower alkyl group.

2. A compound as defined in claim 1 wherein R is hydrogen.

3. A compound as defined in claim 1 wherein R is methyl.

4. A compound as defined in claim 1 wherein R is methyl.

5. A compound as defined in claim 1 wherein R is methyl.

6. A compound as defined in claim 1 wherein R is ethyl.

7. A compound as defined in claim 1 which is 1,1-dimethoxy-2-methyl-3-norbornyl propane.

8. A compound as defined in claim 1 which is 1,1-diethoXy-2-methyl-3-norbornyl propane.

References Cited Moncrieff: The Chemistry of Perfumery Materials (1947), p. 63.

BERNARD HELFIN, Primary Examiner US. Cl. X.R. 252-522 

